1. Field of the Invention
The present invention generally relates to an in-vehicle display device, and more specifically to an in-vehicle display device that includes a display unit provided on a surface of an instrument panel of an automobile and configured to indicate one or more information dots on a windshield of the automobile.
2. Background of the Related Art
Recently, increasing number of various vehicles embrace a display device that incorporates techniques of projecting information directly into a human's field of vision, i.e., a head-up display (HUD) device. The display device of this kind helps improving driver's visibility. A virtual image presented by the display device is superposed on the landscape that can be seen ahead of the vehicle through a windshield of the automobile. The HUD devices of a kind as shown in Japanese Patent Application Laid-Open Publications No. 2002-211274 and No. 2004-130916 has a display unit as a main functional unit dedicated to virtual image display and a reflection member provided in an instrument panel of a vehicle, and light emitted by the display unit is reflected off the windshield or a combiner that protrudes from an upper surface of the instrument panel toward a driver, so that the driver recognizes what is presented within his or her field of vision during driving.
Also, since the driver in a driver's seat gets information mainly through visual perception, visual recognition is of essential importance for the driver. In addition, the driver can readily take a necessary action if the driver can at an earlier stage identify an obstacle that exists in a vehicle's traveling direction. In view of these factors, drive support systems with night-vision capability are advocated that ensures good visibility at night and in all weathers to support safe and careful driving.
A conventional drive support system with night-vision capability has various components including an infrared camera mounted on a front side of the vehicle body, a control unit (microcontroller or microprocessor), and the HUD device. Visual images captured for example by the infrared camera are presented by the HUD device, so that the driver can recognize an obstacle that exists in the vehicle's traveling direction.
A known in-vehicle display device that projects driving information on a windshield is disclosed by Japanese Patent Application Laid-Open Publication No. 2002-019491. The known device has an obstacle detecting unit that detects existence of the obstacle in the vehicle's traveling direction and a line-of-sight detecting unit that detects a direction of a line of sight of the driver. A display position of driving information relevant to the obstacle is moved toward a location of the obstacle and the driver's line of sight is guided toward the location of the obstacle. Also, in an HUD device disclosed in Japanese Patent Application Laid-Open Publication No. 2003-291688, if the obstacle that has been detected is a target object and the driver's line of sight is guided to the target obstacle when a distance between the vehicle and the obstacle becomes shorter than a threshold.
However, in the conventional HUD devices mentioned above, it is necessary to indicate a virtual image in a location relatively distant from the driver so as not to increase driver's burden of focusing his or her eyes on both the real image farther from the driver and the virtual image presented during driving, and one or more reflection members have to be provided to ensure that the virtual image is viewed by the driver at a predetermined distance. Accordingly, the HUD device has to incorporate expensive reflection members that cause a manufacturing cost of the HUD device as a whole to increase. In addition, mounting of the reflection member to the HUD device has to be done with utmost accuracy. Further, when the virtual images are to be projected using the conventional HUD device over a wide area of the windshield, as disclosed for example in the 2003-291688 document, a projector cannot be accommodated inside of the instrument panel, which is undesirable in terms of interior design of the automobile and appearance of a cockpit.
Furthermore, a sufficient space has to be provided inside of the instrument panel in order to accommodate the HUD device inside thereof in a manner that the accommodated HUD device does not interfere with the vehicle body and air-conditioning components.
Also, a size of the conventional virtual image and its display position on the windshield is limited so as not to interrupt a driver's range of vision while driving, and it is difficult for the driver to instantaneously recognize the virtual image while driving. Further, the drive support system with night-vision capability only allows a limited display area with a number of still and/or moving images to a detriment of driver's visibility.